But now I know the knock isn't phasers. It must be a roller rocker. I'll just wait for it to fail.
I believe I paid $14 for a replacement roller rocker and $55 for a valve cover gasket set (O'Reilly auto). I gave $35 for the specialized valve spring and phaser tool set (Amazon.com). It took a couple of hours for me to change at my house. If I remember correctly, a complete set of rockers would have been less than $275. The price to replace aa lash adjusters was similar.
I was very lucky in that when it failed, the failed rocker popped out into a stable position away from moving parts. It's easily possible for a free rocker to destroy other rockers, springs, valves, or the cam. As a general rule, making a repair early is much cheaper than waiting. That is my primary point of this post.
Of course, correct diagnosis comes before anything else. One should never go out and buy parts unless they are proven defective. On my 2011, I was getting warnings concerning a random misfire in cylinder 7 and occasional warnings about fuel mixture problems. I checked plugs, coil, injectors, and wiring and found no problems. I removed the valve cover over cylinder 7 to look, and there it was. I'll attach a pic.
The reason it showed up as a random miss was that the other intake valve still worked. Number 7 was still getting fuel mixture. Just not enough to run at 100%.
The author of the video in Don Hall's post is very good and he has several videos concerning this problem. I would highly recommend you watch.